This locking part typically involves a side window of a motor vehicle driven by an electric motor or the sliding roof of a motor vehicle or a garage door driven by electric motor.
Window lift systems and sliding roof system of motor vehicles are often equipped with an anti-trap mechanism. The function of this mechanism is for example to avoid a hand of a person becoming trapped or to limit the closing force. This anti-trap mechanism includes a mechanical system and control electronics in each case.
Position information is determined during a movement of the locking part in the direction of its opened or its closed state. This information is typically determined using Hall sensors, which detect the rotation of the rotor shaft of the electric motor driving the locking part and output the rotational speed pulses to the control electronics.
In order to obtain a reference position for the position determination specified above, it is already known that the locking part can be moved for example in the direction of its closed state until it reaches a stop position and this stop position can be used as the reference position.
To enable this type of system to be constructed in a simple and cost-effective manner often only a stop position on one side is used, corresponding for example to the closed state of the locking part.
With such a system the problem arises of ensuring that the stop of the looking part actually involves a stop at a mechanical resistance defining the closed position of the locking part and not the locking part stopping against a foreign body, for example a hand of a person. If the stop involves the stop at a foreign body then an incorrect position is fixed as the reference position. This leads to the movement path of the locking part assumed by the control device differing from the actual existing movement path. This can lead to a malfunction of the system, with damage or even destruction of mechanical and/or electrical components of the system also occurring as a result of this malfunction. Injuries to a person whose hand for example gets in the way of a closing motor vehicle window can also not be excluded if the reference position is incorrectly fixed for position measurement.
A method for operating an electric motor-driven window lift for a motor vehicle is known from DE 44 32 955 C2. With this known method, after a button is pressed for the window lift movement the reaching of the window closed position is determined by a motor-stopped sensor. Furthermore an automatic surplus force limitation is provided which on activation initiates stopping and reversing of the direction of the window lift movement. Furthermore in special operating cases such as the end of a power failure for example, signals are generated to restore normal operation. In addition, to make do without a further button for establishing normal operation, first signals which represent the special operation cases and second signals which represent predetermined sequences of actuations of the button for restoring normal operation are fed to a motor controller with memory facilities.